Journal: Geophysics

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Publisher

Society of Exploration Geophysicists

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ISSN

0016-8033
1942-2156

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Publications1 - 10 of 166
  • Optimizing near-orthogonal air-gun firing sequences for marine simultaneous source separation
    Item type: Journal Article
    Mueller, Moritz B.; Halliday, David F.; van Manen, Dirk-Jan; et al. (2016)
    Geophysics
  • Broadband seismology in oil and gas exploration and production
    Item type: Journal Article
    Robertsson, Johan O.A.; Ronen, Shuki; Singh, Satish; et al. (2013)
    Geophysics
  • Accounting for relaxation processes during the pulse in surface NMR data
    Item type: Journal Article
    Walbrecker, Jan O.; Hertrich, Marian; Green, Alan G. (2009)
    Geophysics
  • Noise-based monitoring and imaging of aseismic transient deformation induced by the 2006 Basel reservoir stimulation
    Item type: Journal Article
    Hillers, Gregor; Husen, Stephan; Obermann, Anne; et al. (2015)
    Geophysics
    We have analyzed the time-dependent properties of the ambient seismic wavefield between 0.1 and 8 Hz to detect, resolve, monitor, and image the deformation induced by the water injection associated with the stimulation of the 2006 Deep Heat Mining Project in the city of Basel, Switzerland. The application of passive methods allowed the detection of an aseismic transient of approximately 35 days’ duration that began with the onset of the reservoir stimulation. Peak deformation was reached some 15 days after the bleed-off and after the induced seismicity ceased. We resolved a significant increase in seismic velocities and a simultaneous decorrelation of the noise correlation coda waveforms. The wavefield properties implied that the material response was monitored mainly in the sedimentary layer (<2.5  km) above the stimulated volume that was approximately 4.5 km deep. We inverted the velocity-change and decorrelation data to estimate the spatial distribution of the medium changes. The resulting images showed that the strong velocity variations and medium perturbations were generally colocated with the lateral distribution of the induced seismicity. Positive velocity changes and damage around the injection site indicated subsidence, settling, and compaction of the material overlying the stimulated volume. Our results demonstrate that noise-based analysis tools can provide important observables that are complementary to results obtained with standard microseismicity tools. Passive monitoring and imaging have the potential to mature into routinely applied observation techniques that support reservoir management in a variety of geotechnical contexts, such as for mining, fluid injection, hydraulic fracturing, nuclear waste management, and CO2 storage.
  • Elastic vertically transversely isotropic full-waveform inversion using cross-gradient constraints — An application toward high-level radioactive waste repository monitoring
    Item type: Journal Article
    Manukyan, Edgar; Maurer, Hansruedi (2020)
    Geophysics
    Anisotropic seismic full-waveform inversion (FWI) is a challenging task. In the case of 2D vertically transversely isotropic (VTI) media, there are five independent model parameters. This relatively large number of different parameter types imposes significant trade-off issues and makes the inversion parameterization a challenging task. The problem is less severe in a crosshole configuration, in which a wider angular coverage of the region of interest is available. There exist many suggestions for suitable inversion parameterizations. We have determined that, for a crosshole configuration, a relatively simple velocity-based parameterization provides a good FWI reconstruction of the subsurface. Furthermore, considerable improvements of the tomographic images can be achieved by supplying structural similarity constraints using cross gradients to the inversion problem. With two synthetic data sets, we determine that a structurally constrained VTI FWI workflow produces sharper subsurface images without adversely affecting the parameter trade-off issue. With a second synthetic experiment, we find that structurally constrained VTI FWI is robust to major differences in anomaly locations for different parameter types. We successfully applied the methodology to a crosshole data set acquired to image a downscaled version of a high-level radioactive waste repository. The resulting tomograms allowed a narrow highly fractured zone to be imaged.
  • Source-side spatial wavefield gradients in land seismic exploration
    Item type: Journal Article
    Van Renterghem, Cédéric; Schmelzbach, Cédric; Sollberger, David Andres; et al. (2019)
    Geophysics
  • Data-driven wavefield focusing and imaging with multidimensional deconvolution
    Item type: Journal Article
    Broggini, Filippo; Snieder, Roel; Wapenaar, Kees (2014)
    Geophysics
    Standard imaging techniques rely on the single scattering assumption. This requires that the recorded data do not include internal multiples, i.e., waves that have bounced multiple times between reflectors before reaching the receivers at the acquisition surface. When multiple reflections are present in the data, standard imaging algorithms incorrectly image them as ghost reflectors. These artifacts can mislead interpreters in locating potential hydrocarbon reservoirs. Recently, we introduced a new approach for retrieving the Green’s function recorded at the acquisition surface due to a virtual source located at depth. We refer to this approach as data-driven wavefield focusing. Additionally, after applying source-receiver reciprocity, this approach allowed us to decompose the Green’s function at a virtual receiver at depth in its downgoing and upgoing components. These wavefields were then used to create a ghost-free image of the medium with either crosscorrelation or multidimensional deconvolution, presenting an advantage over standard prestack migration. We tested the robustness of our approach when an erroneous background velocity model is used to estimate the first-arriving waves, which are a required input for the data-driven wavefield focusing process. We tested the new method with a numerical example based on a modification of the Amoco model.
  • Modeling of pure acoustic wave in tilted transversely isotropic media using optimized pseudo-differential operators
    Item type: Journal Article
    Yan, Jun; Liu, Hong (2016)
    Geophysics
    Conventional modeling and imaging for tilted transversely isotropic (TTI) media may suffer from numerical instabilities and shear artifacts due to the coupling of the P- and SV-wave modes in the coupled equations. On the contrary, the decoupled equations for TTI media provide a more stable solution due to the separated P- and S-wave modes. Because the decoupled equations involve complicated pseudo-differential operators in space, it is more convenient to apply the pseudo-spectral method to these equations. However, the second-order time-stepping scheme of the pseudo-spectral method may suffer from time-stepping errors and instabilities for a large time step. We have developed an optimized pseudo-differential operator (OPO) that incorporates not only the spectral evaluation of the pseudo-differential operator but also a temporal correction term that would effectively compensate the time-stepping errors associated with the time-wavenumber domain extrapolation of the wave equation. The OPO was constructed through multiplying the symbol of the OPO by the normalized pseudo-Laplacian operator, which contains a variable compensation velocity. It was efficiently solved through the low-rank decomposition. We have applied OPOs to solve the TTI decoupled equation to simulate the pure acoustic wave. Our 2D and 3D synthetic results demonstrate that the proposed method has high accuracy in time and space with relaxed stability conditions compared with the conventional pseudo-spectral method. The low rank of symbols of OPOs makes the proposed method more efficient than the dispersion relation-based low-rank wave extrapolation and pseudo-analytical methods.
  • A finite-difference iterative solver of the Helmholtz equation for frequency-domain seismic wave modeling and full-waveform inversion
    Item type: Journal Article
    Huang, Xingguo; Greenhalgh, Stewart (2021)
    Geophysics
    We have developed a finite-difference iterative solver of the Helmholtz equation for seismic modeling and inversion in the frequency domain. The iterative solver involves the shifted Laplacian operator and two-level preconditioners. It is based on the application of the preconditioners to the Krylov subspace stabilized biconjugate gradient method. A critical factor for the iterative solver is the introduction of a new preconditioner into the Krylov subspace iteration method to solve the linear equation system resulting from the discretization of the Helmholtz equation. This new preconditioner is based on a reformulation of an integral equation-based convergent Born series for the Lippmann-Schwinger equation to an equivalent differential equation. We have determined that our iterative solver combined with the novel preconditioner when incorporated with the finite-difference method accelerates the convergence of the Krylov subspace iteration method for frequency-domain seismic wave modeling. A comparison of a direct solver, a one-level Krylov subspace iterative solver, and our two-level iterative solver verified the accuracy and accelerated convergence of the new scheme. Extensive tests in full-waveform inversion demonstrate the solver’s applicability to such problems.
Publications1 - 10 of 166